The present invention concerns an injection molding tool plate for use in an injection molding tool for producing molded articles comprising a plurality of handling elements arranged in columns and rows, wherein the spacing r between adjacent handling elements within the row is greater than the spacing s between adjacent handling elements within the columns,
Injection molding is one of the most important processes for the production of molded articles or shaped parts. In that case the molding material which is generally originally present in the form of powder or granular material is heated, plasticized and pressed under high pressure into a corresponding molding tool. The molding material sets in the molding tool and is then removed from the opened tool. By way of example commercially usual PET bottles are produced by stretch blow molding of a hollow body preform or hollow body pre-molding. In that procedure the preform is produced by injection molding in a first step. The stretch blow molding operation which follows the injection molding process can be effected either immediately after production of the preform or at a later time,
A high level of complication and expenditure is needed in the production of the corresponding injection molding molds as the injection molding mold on the one hand must be designed for very high pressures and on the other hand must have suitably heated and/or cooled passages.
Even if the present invention could be used in principle in injection molding tools of any kind it is described hereinafter by reference to an injection molding tool for the production of PET preforms. Such injection molding tools have a large number, for example 96, of cavities into which suitably designed tool cores are introduced. When the tool is closed, that is to say when the core is inserted into the corresponding cavity, a space, the so-called mold space, is formed between the core on the one hand and the cavity on the other hand, and then the plasticized plastic material, for example PET, is injected under high pressure into that space. As soon as the PET preform has sufficiently cooled the mold can be opened and the preform removed. To reduce the cycle times, that is to say the time from one injection process to the next, it is already usual for the preform to be removed from the mold at a very early time, at which the preform is already firm at its outside surfaces, but the inside region thereof is still fluid. The preform is generally transferred in that condition into a so-called removal plate having a set of receiving cavities. In that case the receiving cavity set includes as many receiving cavities as the tool has cores or cavities so that the hardened preform can be transferred from each core into a receiving cavity. Thus for example in the case of the so-called vertical tools, that is to say those injection molding tools which open by a vertical movement of the one tool portion relative to the other, the tool mold is already to be opened after for example 10 seconds, a removal plate with suitable receiving cavities is to be introduced between the tool portions into the mold, the individual preforms are to be allowed to drop into the receiving cavities under the force of gravity, the removal plate with the preforms is to be removed from the tool, the mold is to be dosed again, and the next injection molding process is to be begun. During the next injection molding process the previous preforms remain in the receiving cavities which are usually cooled.
Embodiments are also known in which the individual preforms are removed from the mold by means of a gripper unit and are transferred into the removal plate arranged outside the tool mold.
As the preform must remain in the receiving cavity of the state of the art for cooling purposes for a comparatively long time so that in general the next preform can already be removed from the injection molding tool before the preform has cooled down in the receiving cavity to such an extent that it can be removed without the risk of damage it is already usual to employ removal plates having a plurality of sets of receiving cavities, wherein each set has as many receiving cavities as the injection molding tool provides preforms for each injection cycle. The individual receiving cavity sets are then successively equipped with preforms so that the individual preform can remain in the receiving cavity longer than an injection molding cycle.
In the production of preforms the injection molding tools have two tool halves which can be reciprocated between an open and a closed position. The one tool half has the so-called cavity plate which has a large number of cavities arranged in columns and rows, wherein the spacing r between adjacent cavities within the rows is greater than the spacing s between adjacent cavities within the columns. The other tool half has a core plate which has corresponding cores which are arranged within the cavities in the closed condition of the tool mold. Therefore the cores are also arranged in a large number of columns and rows, wherein the spacing r between adjacent cores within the rows is greater than the spacing s between adjacent cores within the columns. Both the cores and also the cavities are handling elements in the sense used in the present invention. Handling elements are all elements which come into contact with or process the molded articles during manufacture or removal or subsequent cooling.
In general the feed of the plasticized molten PET material is effected by way of openings in the bottom of the cavities. To be able to feed the plasticized molten material uniformly to all cavities the cavity plate has a corresponding hot runner network arranged in the interior of the cavity plate. As the sprue, that is to say the point at which the plasticized molten material is fed to the cavity plate, is generally arranged in the center of the plate the hot runner network extends from the sprue to each cavity, wherein the runners become progressively narrower, the further they are away from the sprue. In the proximity of the sprue however a portion of the hot runner will be of a relatively large cross-section so that adjacent cavities cannot be arranged too closely together in mutually juxtaposed relationship.
For that reason in the described PET tool a spacing of about 140 mm is frequently maintained between the center point of a cavity and the center point of the cavity immediately adjacent in the direction of the row.
In principle uses are also conceivable, in which it is not the cross-section of the hot runner but possibly the cross-section of cooling passages in given regions of the cavity plate or the core plate, that prevents the handling elements from being arranged too close together,
In general the spacing s between adjacent cavities within the columns can be selected to be smaller.
By virtue of the relatively large spacing r between adjacent cavities and cores within the rows the individual receiving cavity sets can be arranged in interleaved relationship so that for example a respective receiving cavity of a second set is arranged between two receiving cavities of a first set respectively. In other words, for example in the case of two receiving cavity sets in the row direction, each second receiving cavity belongs to the first receiving cavity set while the other receiving cavities belong to the second receiving cavity set.
As soon therefore as the injection molding tool opens the removal plate can be moved into the opened tool and receive the preforms. Then, by virtue of the special arrangement of the receiving cavity sets, in the case of two receiving cavity sets each second receiving cavity is occupied by a preform while the other receiving cavities of the removal plate are empty. The removal plate is now moved out of the tool, the tool is closed and the next set of preforms produced. As soon as the mold is opened again the removal plate is moved again between the opened tool halves but this time into a displaced position so that now the preforms of the next set can be transferred into the free receiving cavities of the other receiving cavity set.
As soon as all receiving cavities are occupied and the removal plate is moved out of the tool again the preforms kept longest in the removal plate have to be removed. For that purpose a post-treatment plate equipped with cooling pins and removal pins is oriented with the removal plate in such a way that the cooling pins and the removal pins respectively engage into the preforms held in the removal plate. The cooling pins serve to feed coolant, for example air, while the removal pins can be actuated in such a way, for example by applying a reduced pressure, that they can take the corresponding preform out of the removal plate. In order to be able to remove all preforms from the different receiving cavity sets the post-treatment plate can be oriented in various mutually displaced positions with the removal plate so that, in each of the different positions, the removal pins align with another receiving cavity set and the preforms disposed therein can be removed thereby.
In principle it is desirable for the cavities and cores to be arranged as closely together as possible to reduce material and weight of the injection molding tools.
In general however at least one hot runner for feeding the plasticized molten material extends substantially in the column direction within the cavity plate, and that has the result that the cavities cannot be arranged as close to each other as may he desired in the region of that hot runner. In the state of the art therefore that hot runner establishes the spacing of for example 140 mm between adjacent cavities. The result of this is that the cores must also be at the corresponding spacing, which in turn has the result that the receiving cavities of a receiving cavity set must also he at a spacing of 140 mm from center point to center point. To ensure removal and post-treatment or cooling of the preforms in the removal plate the removal pins and the cooling pins of the post-treatment plate must then also involve the same spacing dimension.